The present invention pertains to a method and apparatus for measuring mass emissions from a vehicle exhaust and, more particularly, to such a mass emission measurement utilizing dilution of the vehicle exhaust with air.
A vehicle exhaust emission analysis technique conventionally measures the concentrations of the component gas emissions in order to determine compliance with environmental standards. Gas concentration measurement, however, is inadequate to determine the true emissions of the vehicle. In order to measure true emissions, it is necessary to measure the mass of emissions and not just the concentration because the concentration is only one parameter of the amount of pollution generated. In order to measure mass emissions, it is necessary to also determine volume, or flow, of the exhaust gas.
One known teaching for measuring mass emission directly measures the flow of gases from the tailpipe using a technique which accounts for the operating environment. This technique is difficult to carry out because the presence of exhaust gases and high heat provides a hostile testing environment. Furthermore, an adapter must be provided which can tightly connect with a wide range of tailpipe configurations. This technique is especially difficult with dual-exhaust vehicles.
Another known technique measures concentration of exhaust gas which has been diluted. This technique requires expensive instruments because they are measuring component gas concentrations which have been diluted to very low concentrations. Furthermore, variations in exhaust gas volume causes concentration of the exhaust gases to vary, which must be taken into account in order to produce accurate results. The analyzer accuracy range must be sufficient to accommodate a low exhaust volume with a vehicle having a low pollution output as well as a high exhaust volume in a vehicle having a high pollution output. This wide sensing range adds to the expense to the instruments. Another known technique for measuring vehicle mass emission uses a carbon dioxide tracing method which determines flow rate by comparing the measured concentration of carbon dioxide in the undiluted vehicle exhaust gas with the measured concentration of carbon dioxide in a dilute mixture of exhaust gas and a diluting gas. The difficulties with such approach are two-fold. The first is that carbon dioxide is present in very low concentrations in ambient atmosphere, such as approximately 400 ppm, or 0.04%. This very low concentration of carbon dioxide in ambient air is inadequate for use in providing an accurate analyzer calibration point. When testing a vehicle, the analyzer would be operating in the single digit percent carbon dioxide range. Therefore, the use of ambient air for calibration would provide too much uncertainty at the calibration point. As a result, a source of carbon dioxide must be provided as a consumable gas in order to accurately calibrate the dilute carbon dioxide analyzer and measure dilution ratio.
The measurement of carbon dioxide in the dilute mixture of vehicle exhaust and dilution air requires filtration of the dilute mixture prior to passing the mixture over the carbon dioxide analyzer, typically a non-dispersive infrared (NDIR) analyzer, in order to remove water vapor from the dilute mixture. Such filtration requires a complicated gas-sampling system, including pumps, filters, solenoids, and the like. Without such filtration, life expectancy of the carbon dioxide sensor is reduced. However, the extra gas-sampling system adds significant cost to the analyzer. Additionally, the delay attendant to such sampling system creates a phasing between concentration measurements taken of the undiluted exhaust gas and those taken of the dilute mixture. The alignment of dilute and undiluted concentration is critical to the accuracy in the assessment of mass emissions. As the complexity of the sample system increases, the more difficult and costly it is to achieve acceptable alignment levels. As a result of cost and complexity, such technology has been practiced only in laboratory settings.
Accordingly, the need exits for a rugged, inexpensive vehicle exhaust mass emission analyzer which provides accurate measurement of vehicle mass emissions without a consumable calibration gas that can be used in laboratory and field emission testing programs.
The present invention provides a method and apparatus for measuring vehicle exhaust mass emissions which is accurate, robust, and low cost and which does not require use of a consumable calibration gas. A method of measuring vehicle exhaust mass emissions according to an aspect of the invention includes sampling undiluted vehicle exhaust and a dilute mixture of vehicle exhaust in dilution air, measuring concentration of gas components of the undiluted vehicle exhaust, measuring concentrations of a particular exhaust component of the dilute mixture and resolving the concentration of exhaust gas components, the concentration of the particular exhaust gas component, and the flow rate of a dilute mixture to mass emissions of the exhaust gas components. The processor obtains compensated values of mass exhaust gas components that are compensated for chemical reaction of the exhaust gas components. The compensated value is a function of at least one undiluted exhaust gas component and is greater than the calculated value for that component.
A vehicle exhaust mass emission analyzer, according to an aspect of the invention, includes an exhaust inlet adapted to collect vehicle exhaust and a dilution air inlet connected with the exhaust inlet to provide a dilute mixture of vehicle exhaust and dilution air. A first analyzer is provided which measures concentration of exhaust gas components from the exhaust inlet. A second analyzer is provided which measures concentration of at least one dilute mixture gas component. A meter is provided which measures flow rate of the dilute mixture. A processor resolves the concentration of the exhaust gas components, a compensated value of the concentration of the at least one dilute mixture gas component, and the flow rate of the dilute mixture to mass emissions of the exhaust gas components. The compensated value is adjusted for chemical reaction of the exhaust gas components and is greater than the uncompensated value.
The present invention provides a method and apparatus for measuring vehicle exhaust mass emissions which is accurate, robust, and low cost and which does not require use of a consumable calibration gas. A method of measuring vehicle exhaust mass emissions according to an aspect of the invention includes measuring the temperatures of the ambient air, undiluted vehicle exhaust, and the dilute mixture of the vehicle exhaust in dilution air, measuring concentration of gas components of the undiluted vehicle exhaust, and measuring flow rate of the dilute mixture. The method further includes resolving the concentration of exhaust gas components, the three temperatures, and the flow rate of a dilute mixture to mass emissions of the exhaust gas components. This may be accomplished using temperature balance equations to determine actual dilution ratio. From the actual dilution ratio and dilute mixture volume, exhaust volume can be determined. From exhaust gas volume and measured exhaust gas component concentrations, exhaust mass emissions can be accurately determined.
A vehicle exhaust mass emission analyzer, according to an aspect of the invention, includes an exhaust inlet adapted to collect vehicle exhaust and a dilution air inlet connected with the exhaust inlet to provide a dilute mixture of vehicle exhaust and dilution air. A first analyzer is provided which measures concentration of exhaust gas components from the exhaust inlet. A second analyzer is provided which measures the temperatures of the non-diluted vehicle exhaust, the ambient dilution air and the diluted exhaust component. A meter is provided which measures flow rate of the dilute mixture. A processor resolves the concentration of the exhaust gas components, the three temperatures, and the flow rate of the dilute mixture to mass emissions of the exhaust gas components.
These and other objects, advantages, and features of this invention will become apparent upon review of the following specification in conjunction with the drawings.